Putting this here so I can say I told you so if I'm right.

As of episode 6, I am predicting that this drama will end with both the ML and the FL breaking up and moving on to the SFL and SML.

Then, maybe after a timeskip, the two off them will see each other from a distance, out in the wild with their respective partners. But they won't approach each other. Instead, they will share a sad smile over that distance, each one acknowledging their long history with one another, what they once were, and the fact that it has come to an end.

Then they'll each walk off with their partners, and the screen will fade to black. The end.

...Or something like that. Not saying I prefer this ending, but I can see them doing it.